Preparation and properties of solution cast films from pilot-scale cottonseed protein isolate

This research defines the value of films made from cottonseed protein isolate (CPI). A high-quality (95% protein content) protein isolate was recovered from glandless cottonseed meal using room temperature water (pH=11), after centrifugation, acid-precipitation, washing, and freeze-drying. Formic acid (FA) was found to be a good solvent for CPI and solutions of 23% solids were made to prepare poured films. FA had not been used as a solvent for CPI previously, and it was found to be capable of forming solutions with solids concentration four times greater than previously reported solvent systems. Dissolution into FA and film production did not affect molecular weight, indicating that hydrolysis did not occur. Six reagents were evaluated as plasticizers for CPI. Of these reagents, glycerol and levulinic acid were selected for additional research. Films having between 5% and 40% plasticizer were made, and the clear, defect-free, hygroscopic films with preferred formulations had good tensile strength (TS), ~ 30 MPa with low elongation (Elo), ~13% at 30% relative humidity (Rh). The TS and Elo of these films were better, and had similar Young’s modulus, when compared to CPI films reported earlier by other researchers. As the Rh increased, the film’s Elo increased while TS decreased. The films had glass transition temperatures of ~110 °C and began to experience a high rate of degradation above 200 °C. The results show a significant improvement in the isolation method and formulation of CPI films with superior tensile properties compared with previous literature methodologies. These improvements are due to the quality of the protein and the use of a superior solvent. These films may ultimately be of value for food packaging applications when the Rh sensitivity is resolved.